Electron configuration of Fe(2+)
The Attempt at a Solution
1s2 2s2 2p6 3s2 3p6 3d3 4s2
But from (https://www.thestudentroom.co.uk/showthread.php?t=1232420),
it says 1s2 2s2 2p6 3s2 3p6 3d6.
isn't electrons fill up 4s shell first, before filling up 3d shell, for more stable arrangement?
or have Cr structure of "4s1 3d5"?